Brain edema after intracerebral hemorrhage (ICH) exacerbates brain injury. The coagulation cascade, especially thrombin formation, plays an important role in brain edema formation after ICH. However, recent studies indicate that low concentrations of thrombin may actually protect neurons and astrocytes from cell death induced by hypoglycemia and ischemia in vitro. The purpose of our present project is to investigate the mechanisms of thrombin preconditioning (TPC)-induced brain tolerance in vivo. Our preliminary studies have demonstrated: 1) TPC significantly attenuates thrombin-induced brain edema, perihematomal brain edema and lysed erythrocyte-induced edema; 2) Thrombin-induced brain tolerance may be associated with heat shock protein (HSP) 27 and/or colligin induction; 3) TPC activates p38 mitogen activated protein kinase (p38 MAP kinase) and extracellular signal regulated kinase (ERK) p44/42 MAP kinase; 4) TPC-induced brain tolerance may be through thrombin receptor activation; 5) TPC also reduces focal ischemic brain edema and brain infarction. Our preliminary data lead us to examine the following hypotheses. 1) To determine whether thrombin induces brain tolerance through activating thrombin receptors. 2) To determine whether TPC induced tolerance is associated with HSP27 and serine protease inhibitor upregulation through the ERK and/or p38 MAP kinase signal transduction pathways. 3) To determine whether thrombin induces phosphorylation of HSP27 through p38 MAP kinase activation and whether HSP27 phosphorylation in turn modulates the actin cytoskeleton dynamics. ICH is a common and often fatal subtype of stroke and produces severe neurologic deficits in survivors. Brain edema after ICH contributes to these outcomes causing both acute herniation-related deaths and long-term neurologic deficits. The long term goal of our studies is to inhibit brain edema formation and limit brain injury after ICH. In this proposal, we will use several well established techniques in this laboratory to determine the mechanisms involved in TPC-induced brain tolerance. It is important to understand the mechanisms behind the thrombin-induced tolerance since they may represent naturally occurring pathways that can be manipulated pharmacologically to limit brain injury after ICH. Our results with TPC are somewhat analogous to results showing a brief ischemic episode can increase tolerance to subsequent severe ischemia, but TPC induced tolerance may be mediated by a specific receptor-activated pathway simplifying identification of the processes involved.